1. Field of the Invention
This disclosure relates to a belt unit, a transfer unit and an image formation apparatus.
2. Description of Related Art
As an example of conventional image formation apparatuses such as a printer, a copy machine, a facsimile machine, and a multifunction machine, an electrophotographic printer forms an image on a paper sheet as follows. First, the surface of a photosensitive drum is uniformly charged by a charge roller, and then is exposed to light from an LED head to form an electrostatic latent image. Next, a development unit develops the electrostatic latent image to form a toner image on the photosensitive drum, and then the toner image is transferred and fixed onto the paper sheet to form the image.
The printer is provided with a transfer belt unit as a belt unit that transfers the toner image to the paper sheet. There are two types of transfer belt units. One is configured to directly transfer the toner image from the photosensitive drum to the paper sheet conveyed by a transfer belt as a belt member. The other is configured to transfer the toner image to a transfer belt, and thereafter transfer the toner image from the transfer belt to the paper sheet. For either type of transfer belt unit, the transfer belt is made to run by a drive roller, an idle roller and the like being rotated.
If while running, the transfer belt meanders by moving in its width direction, the toner image cannot be properly transferred to the paper sheet or the transfer belt.
In view of this, a pulley as a meander restraint member is provided to an end portion of a predetermined one of the drive roller, the idle roller and the like, for example to an end portion of the idle roller, in order to prevent the meandering of the transfer belt (see Japanese Patent Application Publication No. 2011-107340 (Patent Document 1)).